In the Royal Navy, the officer in command of any vessel is considered the captain even if that officer holds a different rank. Royal Navy officers who rank as captains may serve on ships or on land in naval bases or other service establishments.

In former times Royal Navy officers who were captains by rank were distinguished from officers in command of a naval vessel or commanders who received the title of captain as a courtesy by referring to properly ranked captains as post-captains. This practice is now defunct.

The rank insignia features four rings of gold braid with a loop in the upper ring.[1]

When in mess dress or mess undress officers of the rank of captain and above wear gold-laced trousers (the gold lace stripes are nicknamed "lightning conductors"), and may wear the undress tailcoat (without epaulettes).[2]